1. Technical Field
The present invention relates to a battery pack manager.
2. Background Art
A battery pack comprised of nickel-metal hydride batteries has hitherto been used as a power source for a motor in a motor vehicle, like a hybrid electric vehicle and a pure electric vehicle, or as a drive source for a load. A lithium ion battery exhibits higher energy density than that exhibited by other secondary batteries and is also superior to the other secondary batteries in terms of charge/discharge efficiency. For these reasons, substitution of the nickel-metal hydride batteries for lithium ion batteries is under consideration.
A battery pack built in a motor vehicle is made by connecting a plurality of blocks in series, and each of the blocks is further made by connecting a plurality of battery cells in series. In order to control a state of the battery pack or detect an anomaly in the battery pack, a manager is provided on a per-block basis, thereby detecting voltages of the battery cells.
JP 2006-29895 A discloses a required number of integrated circuits for monitoring a battery voltage that are used while connected in series with each other; namely, in a so-called stacked manner. Specifically, a first integrated circuit and a second integrated circuit are provided for series-connected eight battery cells. Provided that the first integrated circuit is a high level integrated circuit and that the second integrated circuit is a low level integrated circuit, each of the high level and low level integrated circuits has, as power terminals, a VDD terminal that is a terminal of the highest electric potential VDD and a VSS terminal that is a terminal of the lowest electric potential VSS. The VSS terminal of the high level integrated circuit and the VDD terminal of the low level integrated circuit are commonly connected together. By way of a resistive potential dividing circuit, a signal output terminal SOUT of the high level integrated circuit and a reference voltage terminal REFU of the low level integrated circuit are connected together between the high level integrated circuit and the low level integrated circuit. A divided potential output terminal of the resistive potential dividing circuit is connected to a signal input terminal SIN of the low level integrated circuit. The configuration makes it possible to transmit specifics of a cell anomaly detected by the high level integrated circuit to a controller by way of the low level integrated circuit.
JP 2007-282413 A provides a disclosure including: taking a voltage across both ends of battery cells of any block in a battery pack into a flying capacitor by means of selective activation of a switching element and further into a microcomputer; managing a state of the battery cells by a management unit provided on a per-block basis; and the respective management units performing processing for letting the battery cells discharge electricity.
Incidentally, the management unit (an integrated circuit) that detects a voltage of each of the blocks constituting the battery pack operates upon receipt of a power supply from a secondary battery that is an object of management. Because of a difference in electric consumption among the plurality of management units, a difference often arises in state of charge (SOC) among the blocks constituting the battery pack.